FUEL & FUEL CYCLE | ADVANCED REACTOR FUEL FABRICATION HALEU UF6 fuel fabrication Enriched uranium hexafluoride (UF6 By Dr. Marina Sokcic-Kostic (Principal Engineer), Christopher Reiser (Physicist),
Karl Froschauer (Deputy Director Business Development), Dr. Georg Brähler (Technology Advisor) NUKEM Technologies Engineering Services GmbH, Karlstein am Main, Germany
MOST ADVANCED OR ESTABLISHED REACTOR concepts can be designed as small modular reactors (SMRs). Considering fuels, the four main SMR designs are based on either ceramic oxide pellets, fuel dispersed in a molten salt, metallic uranium alloys or TRISO-coated uranium kernels. Enrichments in the HALEU range (5% - 20%) are beneficial for SMR fuels, because they have of a higher energy density enabling smaller reactor cores and generally allow for higher burnups. Consequently, refuelling cycles can be extended, and nuclear waste can be reduced in volume. Starting from HALEU uranium hexafluoride (UF6
), the
preferred process is ammonium uranyl carbonate (AUC) deconversion to yield uranium dioxide (UO2
could now be pressed into
pellets and sintered at high temperatures. Furthermore, AUC can be directly calcined to yield triuranium octoxide (U3O8
) with beneficial
physical and chemical properties. If the aim was to produce ceramic oxide SMR fuel, UO2
), which is the input material
for high-temperature reactor (HTR) TRISO fuel element production. Several TRISO-coated particles are processed into fuel spheres or cylindrical compacts for all HTR-SMRs. A major advantage for TRISO fuel applications is the comparably low fluorine content resulting from the AUC
process. UO2 originating from AUC deconversion can easily be fluorinated to uranium tetrafluoride (UF4) by hydrofluoric acid (HF). UF4 is the base material for liquid molten-salt
SMR fuel cores. Finally, metallic uranium can be produced via calciothermic reduction of UF4
. Uranium metal can be
alloyed to fuel liquid metal-cooled SMRs like the sodium- cooled fast reactor (SFR). Overall then, it can be recognised that fuel for all
common SMR types can be produced starting with uranium oxide gained from AUC deconversion.
The major SMR types and their fuel Considering the four major SMR types based on their fuel in the context of current reactor designs the focus lies on the uranium-based fuels mentioned: UO2
pellets, molten UF4
salt, metallic uranium alloys and TRISO particles. Ceramic uranium dioxide pellets are utilised as fuel in the
form of classical cladded fuel rods for light water-cooled SMRs. Currently, the most widespread concept is the pressurized water reactor (PWR) but the boiling water reactor (BWR) also exists as an SMR, though it represents the less common technology. A pioneer in HALEU-fuelled pressurized water SMRs is Russia: An example is the RITM-200, which powers the Arktika icebreaker since 2019.
and SMR ) is considered one of the main
input materials for future fuel production plants for the coming SMR revolution. How can fuel fabrication plants of the past inform their design?
Right: Graphic showing the various SMR fuels that can be derived from AUC deconversion of enriched uranium oxide
46 | May 2024 |
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